[RPG] nything that can create a fire that burns underwater

I would estimate the skill of the creators spellcraft and make a roll each time the item is used underwater. This would make it unreliable, sometime it would work and sometime it would not. This would be more fun and in the spirit of the rule.

If the check succeeds, the spell creates a bubble of steam instead of its usual fiery effect, but otherwise the spell works as described.

Sounds like fire damage to me, but you're burning them with superheated steam instead of flame.